Spring as inductive sensor

Christophe Lapiere

Prodigy 20 points

I just read an article about the LDC1000 in the EDN october issue.

They talk about measuring compression, extention and twist of a spring using the LDC1000.

I didn't find so much informations about this application case in the DS or anywhere.

Is there an application note focused on spring case?

Best regards

Chris

over 11 years ago

0 Evgeny Fomin over 11 years ago

TI__Genius 9300 points

Hi Chris,

It's the same basic idea - we just use the spring as an inductor. When the spring deforms, its inductance will change, and LDC1000 will measure the change.

0 Hawk Tong over 11 years ago in reply to Evgeny Fomin

TI__Intellectual 1840 points

Dear Sir,

what is the mimium inductance could be measured ? Is it possible to detect inductance below 1uH to 100nH ?

any specical tips in desig and implemention ?

regards

Hawk Tong

0 Christophe Lapiere over 11 years ago in reply to Hawk Tong

Prodigy 20 points

Hello,

I've tried with a 250nH (measured with LCR meter) spring and it doesn't work at all.

Spring dimension : 7.6mm diameter * 20mm length

Spring turn : N=11

The little variation of inductance caused by the compression of the spring is not enough to get detect by the LDC1000 even near the Max frequency value.

The quality factor of the LC tank is bad.

I am wondering too if there are any tips and tricks for designing an application based on springs.

BR.

0 Evgeny Fomin over 11 years ago in reply to Hawk Tong

TI__Genius 9300 points

Hello Hawk,

Please see FAQ http://e2e.ti.com/support/data_converters/inductive-sensing/f/938/t/295036.aspx#Q2

0 Evgeny Fomin over 11 years ago in reply to Christophe Lapiere

TI__Genius 9300 points

Hello Christophe,

Please take a look at this thread:

http://e2e.ti.com/support/data_converters/inductive-sensing/f/938/p/295756/1040579.aspx#1040579

While this method is not officially verified by TI yet, it has a lot of merit to it, and worth trying!

0 Evgeny Fomin over 11 years ago in reply to Evgeny Fomin

TI__Genius 9300 points

Hello Christophe,

As a side question - did you manage to make this spring to oscillate at all? I would think it's not possible, but again, I do not know the material and wire diameter...

0 Soumen Nandy over 10 years ago in reply to Evgeny Fomin

Prodigy 10 points

I only experimented with this a bit, but I found that to get any response at all, I needed to insulate the spring with thinned enamel and use a zinc-plated spring for soldering compatibility. I plan to do further experiments, but my preliminary results weren't promising.

0 Evgeny Fomin over 10 years ago in reply to Soumen Nandy

TI__Genius 9300 points

Insulating the spring makes perfect sense if the adjacent windings touch each other - there is direct current path, so there is no coil!

Mechanical solution (crimping/clamping) can be used as an alternative for making contacts to the spring.

What were the results that you do not find promising? I have successfully tested this application in several configurations.

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Spring as inductive sensor